The W3C Markup Validation Service
Posted by jpluimers on 2024/04/03
A while ago I needed to validate some HTML on-line and found the W3C Markup Validation Service.
There are two versions of it that can take different parameters, so below are some permutations of the URLs.
But first why there are two versions, which is explained in W3C Markup Validation Service – Wikipedia
The Markup Validation Service is a validator by the World Wide Web Consortium (W3C) that allows Internet users to check pre-HTML5 HTML and XHTML documents for well-formed markup against a document type definition. Markup validation is an important step towards ensuring the technical quality of web pages. However, it is not a complete measure of web standards conformance. Though W3C validation is important for browser compatibility and site usability, it has not been confirmed what effect it has on search engine optimization.
As HTML5 has removed the use of DTD in favor of a “Living Standard”, the traditional Markup Validation Service is not applicable to these formats. Validation is instead performed using an open-source “Nu Validator”, an instance of which is provided by W3C.
- HTML4/XHTML: [Wayback/Archive] The W3C Markup Validation Service:
https://validator.w3.org/
Default: same as
https://validator.w3.org/#validate_by_uribelow.Note that this tree has no version information of the validator!
- [Wayback/Archive] The W3C Markup Validation Service:
https://validator.w3.org/#validate_by_uri
Enter a URL to have it validated (note it depends on the server always sending out the same HTML)
- [Wayback/Archive] The W3C Markup Validation Service:
https://validator.w3.org/#validate_by_upload
Select a local file, upload it to be validated: unlike
https://validator.w3.org/#validate_by_urithis guarantees repeatability. - [Wayback/Archive] The W3C Markup Validation Service:
https://validator.w3.org/#validate_by_input
Paste your HTML and validate it: unlike
https://validator.w3.org/#validate_by_urithis guarantees repeatability.
- [Wayback/Archive] The W3C Markup Validation Service:
- HTML5: has no default but is versioned (at the time of writing version 22.4.22 of which at least one 22 likely means 2022).
- [Wayback/Archive] Ready to check – Nu Html Checker:
https://validator.w3.org/nu/
Enter a URL to have it validated (note it depends on the server always sending out the same HTML).
- [Wayback/Archive] Ready to check – Nu Html Checker:
https://validator.w3.org/nu/#textarea
Paste your HTML and validate it: unlike
https://validator.w3.org/nu/this guarantees repeatability. - [Wayback/Archive] Ready to check – Nu Html Checker:
https://validator.w3.org/nu/#file
Select a local file, upload it to be validated: unlike
https://validator.w3.org/nu/this guarantees repeatability.
- [Wayback/Archive] Ready to check – Nu Html Checker:
The main validator is closed source, but the “Nu” checker (which probably means “New”, not “Now” like it would mean in Dutch) is open source and written mostly in Java (plus some Python and JavaScript).
- Repository: [Wayback/Archive] validator/validator: Nu Html Checker – Helps you catch problems in your HTML/CSS/SVG
- Documentation: [Wayback/Archive] The Nu Html Checker (v.Nu)
Via [Wayback/Archive] site:https://validator.w3.org – Google Search.
–jeroen
The Wiert Corner - irregular stream of stuff 
Leave a comment